The high economic importance of ornamental plants represents a stimulus for breeders in the research for new cultivars. Among the several employed techniques, gamma radiation induced mutation can bring promising results in Heliconia species. The 50 % lethal dose (LD 50) determination, in in vitro Heliconia bihaicultivation, is the initial step for utilization of that breeding method. The doses: 0; 10; 20; 30; 40 and 50 Gy gamma ray in 25 shoot apexes were tested. The results indicated that LD 50, for this in vitro culture, ranges between 30 and 40 Gy.